How would you broach with a friend your opinion that she needs elocution or similar lessons to get ahead?

[joe friday's grrl]

My friend is 34, and is very bright. She moved to North Carolina from a very small, backwoods town in Mississippi three years ago. She had a very tough life growing up, and ran around with a bad crowd, gambling and doing drugs, until she made a decision to drastically change her life for the sake of her children. She moved here, where her father has been living, to have a little support, and I really admire what she's done in such a short time to turn things around. She's gotten an associate's degree in human services, and has a very good employment record as a community support worker in a group home for former female substance abusers and their children. Recently, she lost a promotion to another employee and, knowing the situation, I'm sure it's only because my friend's grammar and language skills in general are pretty poor. She doesn't use slang as much as she once did, but there are many words she's not even aware of saying improperly. How can I help without insult or embarrassment
Example of the type of thing she might say: "I don't understand cuz I know she like-ted me, and she know I always do good work."